The present invention relates to a method of manufacturing a dynamic semiconductor memory device in which a trench is provided in a memory capacitor region, thereby providing a highly integrated, high-performance device.
A dynamic memory cell consisting of one memory capacitor and one switching transistor can be highly integrated, and can be widely used in memory elements. However, when a unit area of one cell is decreased in accordance with high integration, an area of a memory capacitor is also decreased, thereby considerably decreasing an amount of electrical charge stored in the capacitor. For this reason, recent memory cells have the problems that wrong memory contents are undesirably read out, and the memory contents are destroyed by an electrical charge generated by radiation such as by .alpha.-rays. In order to solve such problems, a method is disclosed in NIKKEI ELECTRONICS, Dec. 20, 1982, pp. 74-75, "Test Manufacture of a Trench Capacitor Cell Suitable for a Large-Capacity Dynamic RAM", wherein a trench is formed in a surface of a memory capacitor portion of a substrate, and an area of the surface of a memory capacitor is increased to increase the capacitance, thereby increasing the amount of a stored electrical charge.
However, this memory structure also has a problem. Since an opening of a mask for forming a trench is formed by mask alignment, an opening cannot be formed into a precise shape in a small memory cell. As a result, an area of a side wall portion of the trench cannot be increased, and therefore, a memory cell having a sufficiently large capacitance cannot be formed. In addition, if the width of an element isolation region becomes narrow, a punch through phenomenon is generated between trenches of memory capacitors adjacent to the region, thereby losing electrical charge and causing data error. In order to prevent this punch through phenomenon, the distance between each adjacent memory cell must be increased, thereby preventing high-integration.